This invention relates to a process for treating lithium cells and cell components so that component materials can be safely recovered for reuse, particularly but not exclusively for treating rechargeable lithium ion cells in which both the anode and cathode comprise insertion materials.
Several of the component materials in rechargeable lithium ion cells are potentially valuable, so that their recovery and reuse is clearly desirable. In particular, the cathodes of such cells may contain metal oxides such as lithium cobalt oxide or lithium nickel oxide (or a mixed oxide of the type LiCoxNi1xe2x88x92xO2); it may be possible to reuse these oxides in this form, although it would usually be preferable if they could be converted to cobalt (II) oxide or nickel (II) oxide (or the mixed oxide) not containing intercalated lithium.
Furthermore the electrolyte may contain ingredients such as lithium tetrafluoroborate or lithium hexafluoro-phosphate which could be reused in making batteries; the latter material however has poor thermal stability, and undergoes hydrolysis in the presence of water. Canon KK have described, in EP 0 613 198A, methods for recovering materials from lithium cells in which an organic solvent is used to dissolve electrolyte material from the cells, but the cathode active material along with polymer binder is merely pulverized.
According to the present invention there is provided a process for treating cells, each cell including particulate cathode material and a binder, an electrolyte, and an anode material, the process comprising the following steps:
a) cutting up the cells in the absence of water;
b) contacting the cells with an organic solvent so as to dissolve out the electrolyte and any electrolyte solvent;
c) then contacting the cells with a solvent for the binder, and thereby separating the particulate material; and
d) reducing the particulate cathode material to remove intercalated ions.
The invention also provides a process for treating cell components comprising particulate cathode material and a binder, the process comprising subjecting the cell component to the steps a) and c), and then performing the step d).
In a preferred method the particulate cathode material is reduced electrochemically. For example lithium cobalt oxide may be reduced to cobalt (II) oxide, thereby also generating lithium hydroxide. The cells may also contain particulate carbon both in the cathode, and as an anode material, the anode incorporating the same binder as in the cathode, so that the particulate material separated in step c) will be a mixture of carbon and cathode material; the particulate carbon does not interfere with the electrochemical reduction process, and indeed it may improve it, as it improves the conductivity of the mixed particle bed. In a modification of this method the particulate material is electrochemically reduced at a circulating particulate bed electrode.
The components of the cells which remain after the two dissolution steps described above are principally the metal foil current collectors from the anode (typically copper) and from the cathode (typically aluminium), the separator, which is typically a non-woven fabric or a micro-porous membrane of a material such as polypropylene, and any cell casing, insulators and seals. These materials can be separated by their density, and possibly by their magnetic properties.
The cutting up of the cells may be performed using a mechanical cutting mechanism, or using a laser. This step is preferably performed in an inert atmosphere, which might for example comprise dry nitrogen. The organic solvent used in step b) to dissolve out the electrolyte preferably also contains no water, and this dissolution step is preferably performed at a temperature which does not exceed for example 60xc2x0 C., so that potentially unstable electrolyte salts such as lithium hexafluoro-phosphate are not degraded. The dissolution process preferably involves re-circulating the solvent through a vessel containing the cut up cells; the solvent may be recirculated sufficiently vigorously that the cut up cells form a fluidised bed.